Method of molding a fuel tank having baffle plates

ABSTRACT

A method of molding a fuel tank wherein two baffle plates mounted on a blow-in are inserted in a molten parison of a thermoplastic resin surrounded by a split metal mold. The split metal mold is closed around the parison and a pressurized fluid is fed through the blow-in into the molten parison to blow-mold the fuel tank. The baffle plates, during the blow-molding, are melt-adhered onto the inner wall of the fuel tank. A blow-molded fuel tank containing two baffle plates adhered to the inner wall of the fuel tank is obtained.

INDUSTRIAL FIELD OF UTILIZATION

The present invention relates to a method of molding a fuel tank havingbaffle plates and, more specifically, to a method of molding a fuel tankby the blow-molding method and, at the same time, mounting baffle plateson the inner surface of the fuel tank as a unitary structure.

PRIOR ART

Plastic fuel tanks such as automotive fuel tanks have been provided withbaffle plates on the inside thereof in order to improve mechanicalstrength, and to prevent unpleasant sound that is generated when thefuel pitches and rolls in the tank while the vehicle is running and tostabilize the internal capacity of the tank.

A conventional method of molding a fuel tank with baffle plates consistsof using a metal mold having convex portions that correspond to theplates, and effecting the blow-molding while arranging in the metal moldthe parison that is formed by extrusion-molding or injection-molding athermoplastic resin.

According to the above method, however, the root portions of the baffleplates tend to lose thickness, limitation is imposed on the size of thebaffle plates, and technological difficulty is involved in molding twopieces of baffle plates simultaneously.

GIST OF THE INVENTION

The object of the present invention therefore is to provide a method ofmolding a fuel tank having baffle plates, which effectively solves theabove-mentioned problems inherent in the prior art.

According to the present invention, there is provided a method ofmolding a fuel tank comprising inserting a blow-pin in a molten parisonof a thermoplastic resin from the lower side thereof, said blow-pinhaving a plurality of grooves formed therein downwardly extending fromthe tip of said blow-pin and having different lengths relative to eachother, mounting a plurality of pre-molded baffle plates on said blow-pinvia the plurality of grooves, closing the split metal molds under thiscondition, feeding a pressurized fluid thereto, and melt-adhering thebaffle plates onto the inner surface of the fuel tank while said fueltank is being molded.

This is, according to the present invention, it is allowed to provide aplurality of, for example, two pieces of baffle plates in the fuel tanksimultaneously with the molding of the fuel tank without resulting inthe formation of very thin portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view of a baffle plate molded article used inthe present invention;

FIG. 2 is a plan view of the baffle plate molded article used in thepresent invention;

FIG. 3 is a diagram illustrating another baffle plate molded articleused in the present invention;

FIG. 4 is a side sectional view illustrating a blow-pin used in thepresent invention;

FIG. 5 is a plan view of the blow-pin that is used in the presentinvention;

FIG. 6 is a diagram showing the step of blow-molding according to thepresent invention; and

FIG. 7 is a diagram showing a fuel tank produced according to thepresent invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In the present invention, examples of the resin material for makingbaffle plates and fuel tank include any thermosetting resins that can beblow-molded such as polyolefin resins, e.g., low-, medium- andhigh-density polyethylenes, a polypropylene, an ethylene-α-olefincopolymer, a thermoplastic polyester, a polyamide resin, etc. Amongthem, a polyolefin resin is preferably used. Moreover, the thermoplasticresins must exhibit not only resistance against environmentally causedstress and cracks (ESCR property) for light oils that are now chieflyused as fuels and methanol that has been studied to be used as a fuel inthe future, but also gas barrier property, impact resistance, heatresistance and weatherability. Among the polyolefin resins, thehigh-density polyethylene is preferably used from the standpoint of suchproperties. As the baffle plates, in particular, there can be preferablyused the high-density polyethylene having a melt flow rate (MFR) of 0.01to 10 g/10 min. and particularly 0.1 to 10 g/min. under the load of 2160g and a density of 0.94 to 0.97 g/cm³. As the fuel tank, there can bepreferably used the high-density polyethylene having an MFR of 1.0 to 10g/10 min. and particularly 2 to 5 g/10 min. under the load of 21.6 kg,and a density of 0.94 to 0.97 g/cm³.

The invention will now be described based on embodiments shown in theaccompanying drawings.

According to the method of the present invention, the baffle plates arefirst molded before being melt-adhered to the interior of the fuel tank.FIG. 1 is a side sectional view of the baffle plates and FIG. 2 is aplan view thereof. As will be obvious from FIGS. 1 and 2, the baffleplates (generally designated at 1) consist of a hollow tubular supportportion 2 and a pair of plate portions 3a and 3b that outwardly extendin the direction of diameter thereof. The tubular support portion 2 hasprotuberances 4,4 formed on the inner surface thereof, so that it can bemounted on a blow-pin that will be described later. In FIGS. 1 and 2,the plates are provided in a pair. The plates, however, may be providedin two or more pairs as shown in FIG. 3.

The baffle plates can be easily molded by a molding method which isknown per se, such as extrusion molding, injection molding or a likemethod.

According to the present invention, the baffle plates are mounted on theblow-pin. Here, it is desired that the baffle plates are pre-heated inan oven maintained at about 100° C. for about 15 minutes. FIG. 4 is aside sectional view of the blow-pin and FIG. 5 is a plan view thereof.That is, the blow-pin (generally designated at 5) has a pressurizedfluid feeding portion 6 formed on the inside thereof and further has anopening 7 formed at the upper end thereof. The pressurized fluid such asthe air is released to the external side through the opening 7, andwhereby the so-called blow molding is carried out.

Furthermore, long grooves 8a and short grooves 8b are alternatinglyformed on the outer surface of the blow-pin 5 downwardly extending fromthe upper end thereof. The blow-pin 5 is inserted in the tubular supportportion 2 of the baffle plates 1, whereby the protuberances 4 engagewith the grooves, and the two pieces of baffle plates 1 are mounted onthe blow-pin 5.

That is, the two pieces of baffle plates are held by the long grooves 8aand short grooves 8b, respectively (the baffle plate held by the longgrooves 8a is located at a lower portion of the blow-pin 5 and thebaffle plate held by the short grooves 8b is located at an upper portionof the blow-pin 5).

According to the present invention, the fuel tank is molded by theblow-molding by using the blow-pin 5 on which are mounted two pieces ofbaffle plates 1.

This step is shown in FIG. 6.

That is, in FIG. 6, a hollow tubular molten parison 11 (parison resintemperature is 200° to 240° C.) is extruded from an extruder 10, and theblow-pin 5 on which the baffle plates 1 are mounted is inserted in themolten parison 11. Split metal molds 12, 12 are arranged on the outsideof the molten parison 11, and are closed under the condition where theblow-pin 5 is fitted in the molten parison 11. The pressurized fluidsuch as the air is blown through the blow-pin 5 in order to mold thefuel tank and, at the same time, to melt-adhere the baffle plates 1 ontothe inner wall of the tank.

After the molding is finished, the blow-pin 5 is pulled out thereby toobtain a fuel tank 13 having baffle plates 1 as shown in FIG. 7.

In the above-mentioned step, it is desired that tiny protuberances 15are formed on the surfaces of the split metal molds 12 that come incontact with the baffle plates 1. The protuberances enable the baffleplates 1 to be effectively melt-adhered.

In the above-mentioned step, the fuel tank was produced having twopieces of baffle plates. It is, of course, allowable to produce the fueltank having more baffle plates, such as three or more pieces of baffleplates. In this case, the number of grooves formed in the blow-pinshould be increased depending upon the number of the baffle plates.

In accordance with the present invention mentioned above, there wasproduced a fuel tank having a content of 100 liters, a weight of 7.5 kgand two baffle plates (0.6 kg) by using the resin described below and ablow-molding machine manufactured by Nippon Seikosho Co. "NB60P115AC25"(mold fastening force 60 tons, screw diameter 115 mm, accumulator 25L).

RESIN USED

Main Body

A high-density polyethylene having an MFR (load 21.6 kg) of 4 g/10 min.,and a density of 0.956 g/cm³.

Baffle Plates

A high-density polyethylene having an MFR (load 2160 g) of 5.5 g/10min., and a density of 0.968 g/cm³.

The thus obtained fuel tank possessed a minimum thickness of greaterthan 3 mm with no extremely thin portions, and was strong enough.

According to the present invention, the metal mold used for the moldingoperation needs not be provided with protuberances that correspond tothe baffle plates. It is therefore allowed to obtain a fuel tank whichas a whole has a uniform thickness without extremely thin portions andto provide two pieces of baffle plates inside the fuel tank while it isbeing molded, contributing to greatly enhancing the operationefficiency.

What is claimed is:
 1. A method of blow-molding a fuel tank comprisingthe steps of:providing pre-molded baffle plates having a hollow tubularportion including an inner surface and plate portions extendingoutwardly from said tubular portion and the inner surface of saidtubular portion having protuberances, and providing a blow-pin having atip and an outer surface including a plurality of grooves in said outersurface extending downwardly from said tip, mounting a plurality of saidpre-molded baffle plates on said blow-pin by having the protuberances onthe baffle plates engage the grooves in the blow-pin; inserting saidblow-pin with the baffle plates in a molten parison of a thermoplasticresin; and closing a split metal mold from outside of the molten parisonat the time of feeding a pressurized fluid into the mold via theblow-pin so that the baffle plates melt-adhere onto an inner surface ofthe fuel tank to be molded.
 2. A molding method according to claim 1wherein said blow-pin has a plurality of grooves of alternatingdifferent lengths, relative to each other, extending downwardly from thetip of said blow-pin.
 3. A molding method according to claim 1, whereinsaid thermoplastic resin is a high-density polyethylene having an MFR offrom 1.0 to 10 g/10 min. under the load of 21.6 kg, and a density of0.94 to 0.97 g/cm³.
 4. A molding method according to claim 1, whereinsaid baffle plates are made of a high-density polyethylene having an MFRof 0.01 to 10 g/min. under the load of 2160 g, and a density of 0.94 to0.97 g/cm³.
 5. A method for blow-molding the main body of a fuel tankcontaining baffle plates which comprises the steps of:providingpre-molded baffle plates having a hollow tubular portion including aninner surface and plate portions extending outwardly from said tubularportion and the inner surface of said tubular portion havingprotuberances, and providing a blow-pin having a tip and an outersurface including a plurality of grooves in said outer surface ofalternating different lengths relative to each other extendingdownwardly from said tip, mounting a plurality of said pre-molded baffleplates on said blow-pin by having the protuberances on the baffle platesengage the grooves in the blow-pin, inserting said blow-pin with thebaffle plates mounted thereon into a molten parison of a thermoplasticresin which is surrounded by a split fuel tank metal mold, having anopening for the blow-pin, closing the split mold, feeding a pressurizedfluid through the blow-pin into the molten parison to blow-mold themolten parison and to melt-adhere the end portions of the baffle platesonto the inner surface of the fuel tank.
 6. A molding method accordingto claim 5, wherein said main body is made from a high-densitypolyethylene thermoplastic resin having an MFR of from 1.0 to 10 g/10min. under the load of 21.6 kg, and a density of 0.94 to 0.97 g/cm³. 7.A molding method according to claim 5, wherein said baffle plates aremade from a high-density polyethylene thermoplastic resin having an MFRof 0.01 to 10 g/min under the load of 2160 g and a density of 0.94 to0.97 g/cm³.